The heat developable light-sensitive materials are known in the art, and the heat developable light-sensitive materials and processes thereof are described, for example, in Shashin Kohqaku no Kiso (Higinen Shashin) (The Fundamentals of Photographic Engineering (Nonsilver Photograph)), pages 242 to 255 (1982), Corona Publishing Co. Ltd and U.S. Pat. No. 4,500,626.
In addition, methods for forming dye images, for example, by the coupling reaction of oxides of developing agents and couplers are described in U.S. Pat. Nos. 3,761,270 and 4,021,240. Further, methods for forming positive color images by the light-sensitive silver dye bleaching process are described in U.S. Pat. No. 4,235,957 and the like.
Furthermore, a method has recently been proposed in which a diffusive dye is imagewise released or formed by heat development and the diffusive dye is transferred onto a dye fixing element. According to this method, either a negative dye image or a positive dye image can be obtained by changing the kind of dye-donating compound used or the kind of silver halide used. Further details thereof are described in U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,137 and 4,559,290, JP-A58-149046 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-60-133449, JP-A-59-218443, JP-A-61-238056, EP-A-220746A2, JIII Journal of Technical Disclosure No. 87-6199 and EP-A-210660 (A2).
Also for methods for obtaining positive color images by heat development, many methods have been proposed. For example, U.S. Pat. No. 4,559,290 proposes a method of allowing a compound obtained by converting a so-called DRR compound to an oxide type having no color image releasing ability to coexist with a reducing agent or a precursor thereof, oxidizing the reducing agent by heat development in accordance with the exposure amount of a silver halide, and reducing the oxidized compound with the remaining reducing agent not oxidized, thereby permitting a diffusive dye to be released. Further, EP-A-220746A and JIII Journal of Technical Disclosure No. 87-6199 (Vol. 12, No. 22) describe heat developable color light-sensitive materials using compounds which releases diffusive dyes by reductive cleavage of N--X bonds (wherein X represents an oxygen atom, a nitrogen atom or a sulfur atom) as compounds which releases diffusive dyes by a similar mechanism.
In general, in the exposure of heat developable light-sensitive materials having a size exceeding A3, the so-called outer drum system exposure is usually employed in which light-sensitive materials are exposed while being wrapped around a drum, because it is difficult to transport the material with plane conveyance. However, the outer drum system exposure providing high resolution has the problem of time consuming. In order to solve this problem, it is proposed to increase the number of revolution of a drum. However, this is liable to causes the problem that it becomes difficult to fix light-sensitive materials to the drum, causing an increase in cost, that the exposure time per exposure point decreases so that the resulting sensitivity or gradation becomes unfavorable, that the developing speed reduces, or that the exposure temperature dependency increases.
On the other hand, as a method for decreasing the exposure time, there is the multiple-beam exposure method of exposing a plurality of exposure points at once. In this exposure method, it is possible to decrease the whole exposure time while decreasing the number of revolution of a drum. In the multiple-beam exposure, a multiple exposure effect of different time intervals as compared with other exposure points is given at exposure points at both ends in an arranged direction of multiple beams from the exposure of the exposure points adjacent to an exposure point to which attention is given. In this exposure method, an exposure head having a plurality of beam light sources is used for obtaining the multiple beams.
Further, a method of arranging exposure beams in a manner different from the conventional one to conduct the so-called interleave system exposure, thereby decreasing the difference in exposure history is described in IS & T's International Congress on Advances in Non-Impact Printing Technologies, page 337 (1994).
The overlapping of exposure beams and the effect of multiple exposure are described in PCT International Publication No. 95/31754 and JP-A-4-51043, which are inventions for monobeam exposure and make no reference to the problems which arise by multiple exposure at all.
Further, JP-A-2-18548 reports that changes in photographic characteristics caused by multiple exposure in scanning exposure are reduced by doping a silver halide emulsion with a heavy metal, but does not mention the problems which arise by multiple exposure at all.
JP-A-7-234371 reports an image forming apparatus for controlling the overlapping of light beams to inhibit the uneven density due to multiple exposure effect in scanning exposure using a monobeam, but is silent on the problems which caused by multiple channel exposure using multiple beams.
JP-A-4-249244 discloses an improvement in a developing solution as a method for inhibiting deterioration of the photographic characteristics which occurs in conducting scanning exposure having high illuminance and an overlap of a short period of time, but describes no improvement by an exposure method and makes no reference to multiple channel exposure at all.